This disclosure pertains to mechanisms and systems for moving optical elements in general and in particular to a system using a Halbach array for moving an optical element.
Systems and mechanisms for moving optical elements in and out of locations such as switching between optical filters or optical elements (e.g., lenses, mirrors, prisms, etc.) in and out of an optical path are in increasing demand for various applications including optical imaging, optical surveillance, etc. The simplest moving or switching systems or mechanisms utilized for moving optical elements or for switching between optical elements do not contain any provision for reducing the reaction forces and moments. For systems that are not sensitive to vibrations or systems that do not require the switch to occur in a very short period of time, this simple approach may be adequate. However, as systems increase in performance they can become more susceptible to vibration and may require a more sophisticated approach.
In some conventional systems, a reaction mass is added to the switching mechanism. Instead of applying a torque between the moving element and the base, a torque is applied between the moving element and the reaction mass. The reaction mass moves in an opposite direction from the moving element and, theoretically, no torque is applied to the base. This approach has various disadvantages, the most severe of which is that the mass is usually approximately equal in size and weight to the primary moving element. The added size, weight and complexity of the reaction mass make packaging difficult and add significant weight to the system. The power consumption of this type of mechanism can also be higher than an equivalent mechanism without a reaction mass. This approach has been used extensively on gimbals and beam steering mirrors.
In systems where there are at least two elements and one of them is always deployed and the other elements are retracted, the torque applied to the element that moves from deployed to retracted can be used to cancel torque of the element that moves from retracted to deployed. This approach is essentially the same as the reaction mass approach described above except that another mechanism which is mounted to a common base is used as the reaction mass. Instead of a torque applied directly between the primary moving element and the reaction mass (requiring one actuator), each of the two moving elements applies a torque to a common plate (requiring two actuators). Because the two mechanisms are rotating in opposite directions, it is possible to cancel the reaction torques resulting in a reaction-less system.
In the systems described above, an actuator is usually the sole source of the torque that moves the masses from one position to another. The actuator typically is the dominant source of heat dissipated in the mechanism. In many systems it is highly desirable to minimize the power consumed by the mechanism. In order to reduce the torque supplied by the actuator, and thus the power dissipated by the mechanism, attempts have been made to add passive energy storage elements to the mechanism that will result in a natural tendency to oscillate.
One such mechanism is a non-contacting magnetic latch (NCML). The NCML mechanism primarily makes use of a torsion rod between the moving element and the base to store most of the energy required to perform the switch. The torque profile of the spring is chosen so that the natural oscillation of the spring-mass system naturally carries the moving element between the retracted and deployed states in the desired switch time while requiring minimal actuator torque. In order to hold the mechanism in either the deployed or retracted position, a NCML is used. The latch is designed with coils that provide a means for releasing the rotor by energizing a coil which produces a magnetic field that opposes the magnetic field of the latch's permanent magnet. The latch torque is thus lowered to below the amount required to counteract the spring and the moving element is allowed to swing to the other operating position where it is caught by a similar active latch. The reaction torque of the mechanism is reduced by always operating two mechanisms in opposite directions.
Another such mechanism, referred to as the “Flexure mechanism,” suspends the rotor on a cross-blade flexure which also serves as the energy storage element. A passive, non-contacting magnetic latch is provided to cancel the torque of the flexure at the two operating positions in order to create detents at the operating positions. The torque provided by the latch plus the flexure (collectively referred to as the “passive torque”) provides a source of stored energy which allows the rotor to switch between the two operating positions with minimal additional torque. The flexure and magnetic latch torque vs. deflection angle profiles are designed to provide a passive torque profile that is optimized to minimize the amount of power required to move the mechanism between its two operating positions. A servo which includes a brushless DC motor and angle sensor is used to control the motion of the rotor. Similar to the NCML mechanism, the reaction torque of this mechanism is also reduced by always operating two mechanisms in opposite directions.
What is needed is an optical switching system for moving optical elements that is configured to, inter alia, cancel reaction torques generated during movement of the optical elements by counter rotating the optical elements.